1. Field of the Invention
The present invention generally relates to methods and systems for well intervention operations in subsea wells, and more particularly to a system and method for removing and setting crown plugs from a subsea installation, such as a horizontal x-mas tree.
2. Background
In order to perform well intervention operations in subsea wells, it is necessary to gain access to the well either by opening some valves (for the so-called Vertical or Conventional x-mas trees) or by removing some plugs, commonly referred to in the art as crown plugs (for the so-called Horizontal x-mas trees). Removal and installation of these plugs is normally performed by slickline, braided line, wireline or coiled tubing (“CT”). In some cases, the removal or installation of a plug can be difficult, due to presence of corrosion, encrustation, debris, differential pressure across the plug, etc.
The problem of removing and installing crown plugs in horizontal x-mas trees has been investigated by several companies involved in subsea intervention, and several existing issued patents or patent applications exist covering different systems and methods to perform these operations, as follows:
Patent application WO2005/103442 entitled “PLUG SETTING AND RETRIEVING APPARATUS” assigned to EXPRO describes an apparatus for, and a method of, setting a plug in or retrieving a plug from a horizontal x-mas tree. The apparatus of WO2005/103442 comprises a housing with a throughbore adapted to be releasably connected at a first end to a horizontal x-mas tree, the housing including an at least one axially moveable member which also includes an at least one radially moveable element and a tool deployable within the housing throughbore by an elongate support and adapted to be releasably connected to the plug.
Patent application WO2006/061645 entitled “PLUG INSTALLATION AND RETRIEVAL TOOL FOR SUBSEA WELLS” assigned to FMC relates to installing or extracting a plug from a subsea well. A plug retrieval and installation tool of WO2006/061645 comprises a housing that is lowered on a lift line or riser and connected to subsea production equipment such as a tree and wellhead housing in use. In addition, a plug manipulator of WO2006/061645 can be extended to install, or retracted to retrieve, a plug-type barrier, that is detachably mounted to the housing so that it can be retrieved independently of the housing.
Patent application WO2007/067786, entitled “PLUG RETRIEVAL AND DEBRIS REMOVAL TOOL” also assigned to FMC relates to methods and tools for retrieving wire line plugs from subsea wells, which allows debris to be removed from on top of the plugs and riser hydrostatic pressure effects to be overcome. An apparatus adapted for removing a plug from a subsea Christmas tree is disclosed in WO2007/067786 which includes a housing, a distal end of the apparatus that is adapted to engage the plug and a fluid passage formed in the housing for use in directing a stream of fluid toward the plug to remove debris from above the plug.
Issued U.S. Pat. No. 6,719,059 entitled “PLUG INSTALLATION SYSTEM FOR DEEP WATER SUBSEA WELLS” assigned to VETCO GREY, issued patent U.S. Pat. No. 7,121,344, entitled “PLUG INSTALLATION SYSTEM FOR DEEP WATER SUBSEA WELLS” also assigned to assigned to VETCO GREY, and patent application US2007/0034379 entitled “PLUG INSTALLATION SYSTEM FOR DEEP WATER SUBSEA WELLS” describe a plug retrieval and installation tool used with a subsea well having a production tree, a tubing hanger, a passage that extends vertically through the tubing hanger and the tree, and a plug located within a plug profile in the passage within the tubing hanger. The plug retrieval device has a housing and connector that is lowered on a lift line onto the upper end of the tree, wherein the connector, drive mechanism and retrieval member are powered by an ROV.
All these systems and methods are quite complex, require the use of dedicated hardware, and the deployment of heavy and bulky equipment which then needs to be retrieved once the plugs have been removed, thus affecting the overall efficiency of the intervention operations.